The present invention relates to an electrical power supply converter coupled to a source of electricity and to an electricity feed line such as a bus.
In the field of missions by satellites in low earth orbit (LEO), the general practice is to use a bus that is powered without regulation, as was the case in the SPOT/ERS/PPF missions and is now the case in the new PROTEUS or GLOBALSTAR mini-satellite. The reason is the high ratio between eclipse time and sun time for such missions and the resulting needs concerning the charging and discharging cycle of the battery. Coupling the battery to the bus eliminates any need for battery discharge elements, and battery charging is controlled by a shunt which presents relatively high efficiency. Such a system is shown in FIG. 1.
That solution presents drawbacks which are well known and which are particularly troublesome in certain projects such as PPF:
the mismatch between the voltage and the array of solar sensors leads typically to the array of solar sensors being overdimensioned by at least 5% to 10%;
the electronics must be dimensioned to operate at the lowest available battery voltage;
the peak power that can be given by heater elements is variable;
protection is difficult to implement; and
the quantity of regulation that is necessary on each converter (e.g. 22 volts (V) to 37 V for the SPOT/PFF satellite), and the fact that for the filters, the size of the inductances is determined by the current at the lowest voltage while the size of the capacitors is determined by the maximum voltage on the bus.
A certain number of new projects (SKYBRIDGE, ATV) have turned towards implementing regulated buses in order to achieve their missions.
One such regulated bus is described in French patent No. 2 785 103 filed in the name of the Applicant company. That solution is not easily applicable to the case where battery voltage is higher than bus voltage as is generally the case in the ATV, SPACE BUS 3000, SOHO, XMM, INTEGRAL, etc. . . . systems. For such projects, the method used has been either a so-called xe2x80x9chybridxe2x80x9d bus or else a bus that is fully regulated with a shunt, battery charge regulation (BCR) and battery discharge regulation (BDR).
A technique that can be used with a battery voltage higher than the bus voltage is described in French patent No. FR-2 777 715 also filed in the name of the Applicant company. That concept requires the shunt to be operated sequentially. It makes it possible to achieve low losses while the shunt is in operation, but it does not make it possible to avoid implementing battery charge regulation (BCR) and it was designed more particularly for telecommunications satellites in geostationary orbit for which only a limited amount of power needs to be available for charging the battery, given that charging can be spread out over a period of 23 hours with only 1 hour of eclipse.
A conventional regulated bus architecture is shown in FIG. 2, for the case of battery voltage being greater than bus voltage.
That architecture makes use of three different converters: the shunt, the charger, and the discharger. One such design is implemented for example in SPACE BUS 3000 or in XMM/INTEGRAL. The shunt is generally a switched sequential shunt, the discharger is a voltage-lowering (xe2x80x9cbuckxe2x80x9d) type converter, the battery charger is a voltage-increasing type converter, being either a voltage-raising (xe2x80x9cboostxe2x80x9d) type converter proper or else a voltage-lowering converter operating in push pull (xe2x80x9cbuck push pullxe2x80x9d). As can be seen, that design needs three different converters to be implemented, each of which forms an amplifier between the main error amplifier (MEA), the bus, and/or the solar array and the battery. In addition, the charger takes its energy from the bus, i.e. energy which has been obtained after the losses generated by the shunt. Efficiency is generally high, but on a 28 V bus, for example, it may be that it does not exceed 96%.
An object of the present invention is to provide a converter enabling a bus to be regulated with a battery whose voltage is higher than that of the bus, while also simplifying the architecture.
The idea on which the invention is based is to implement an electrical module presenting only two active switches for the purpose of performing all three functions: shunt; BCR; and BDR.
U.S. Pat. No. 5,359,280 (SPACE SYSTEMS/LORAL) discloses a voltage converter for powering the bus of a satellite and which presents only two switches, one for charging and the other for discharging the battery.
The architecture of that converter does not enable the shunt function to be obtained, which function is necessary for controlling excess source energy.
Furthermore, it does not enable the converter to be segregated from the bus, e.g. by means of a protective diode. This is due to the fact that the current needs to flow in both directions from the bus.
The present invention makes it possible to obtain all of the desired shunt and battery charge and discharge functions with a module of very simple architecture coupled with a control circuit whose architecture is also simple.
The invention thus provides a converter comprising at least one converter module presenting at least one electricity feed terminal for coupling to an electricity generator such as a solar generator and to an electricity feed line such as a bus, and including at least one series switch and at least one parallel switch, the series switch being connected in series between the electricity feed terminal and a first inductor, itself connected in series with an electricity source including at least one battery, the first series switch and the first inductor forming a series branch, and the parallel switch being connected in parallel between said series branch and ground, said switches of said module being controlled in phase opposition by a control circuit presenting a first control state in which said switches are operated in a first or xe2x80x9cvoltage-loweringxe2x80x9d mode of operation in which electrical current flows from the electricity generator to the electricity feed line, and a second control state in which said switches are operated in a second or xe2x80x9cvoltage-raisingxe2x80x9d mode of operation in which said current flows from the electricity source towards the electricity generator, wherein the parallel switch is connected in a parallel branch between said electricity feed terminal and ground, and wherein the control circuit presents a third or xe2x80x9cshuntxe2x80x9d control state in which the parallel second switch is closed and the series switch is open.
In a preferred embodiment, the control circuit presents a first amplifier (for example common to a plurality of modules) which compares the voltage of the feed line with a reference voltage, and whose output is applied to an input of a second amplifier whose other input receives a signal representative of current output from the module in the electricity feed line. This serves to control the charging and discharging modes of the electricity generator.
In the converter, the control circuit presents a third amplifier whose output induces said third mode of operation when a charging current delivered by the module in the second control state exceeds a given threshold. The choice of this condition is particularly advantageous because providing there is enough electricity available for charging the battery, then the electricity demand of the bus is also satisfied, which means there is no need to impose other conditions on operation in shunt mode.
In the converter, at least one converter module presents a plurality of electricity feed terminals, and for each of said electricity feed terminals there is a series switch forming a series branch together with said first inductor between said terminal and the battery, and a parallel switch forming a parallel branch between said terminal and ground.
In a particular embodiment, the parallel switch(es) is/are connected in series with a second inductor. A capacitor whose terminals are connected between a terminal of the first inductor not connected to the electricity generator, and a terminal of the second inductor not connected to ground.
Advantageously, the converter presents a protective diode which makes it possible to segregate the bus from the converter. This makes it possible to charge the battery in parallel without having a charger converter connected to the bus. In addition, in the event of a module failing, the capacity of the bus is not short-circuited.